Dear Doctor: I've been feeling a bit down lately, and I read that even one hour a week of exercise could reduce depression. How much exercise is optimal to reduce the likelihood of depression?

Dear Reader: We're very sorry to hear that you're struggling, but we are glad that you're open to the idea of physical exercise as a way to improve your mood. In addition to therapy and medication, a combination that offers relief to millions of Americans who suffer from depression or anxiety, studies continue to show that regular exercise can have a beneficial effect on mood and emotional well-being.

The idea of a sound body leading to a sound mind dates back to at least the ancient Greeks. In labs and think tanks throughout the world, scientists have been exploring the connection between exercise and mood for decades. Here in the United States, where health and fitness fads sweep through popular culture like clockwork, plain old exercise remains a constant among the more exotic (goat yoga) and outlandish (sauna suits) approaches that come and -- thankfully -- go.

The latest confirmation of the existence of the mind-body connection comes from a group of scientists who took a new look at data collected from more than 33,000 adults living in Norway. The study subjects, none of whom had mental health or physical issues, were followed for 11 years. During that time, researchers monitored the onset of depression or anxiety among members of the group. They also tracked physical activity.

Their finding that regular exercise had a positive effect on mood wasn't a big surprise. What was startling was just how little physical activity it took for the study participants to experience the mental health benefits.

According to the analysis of the 11 years of data, participants who exercised as little as one hour per week had a 44 percent lower risk of developing depression during the term of the study than the those who remained sedentary. On top of that, exercise intensity appeared not to play a role: Mild and moderate exercise was just as effective as strenuous workouts.

And while increased intensity and duration of physical activity do yield physical benefits, researchers concluded that when it came to protection against depression, mental health benefits leveled off beyond two hours of activity per week. The other interesting outcome of this second look at the data was that while exercise did offer a degree of protection against depression, it had no effect on anxiety.

If your next question is why just one hour of exercise a week can be beneficial to mental health, the authors of the study admit they don't know. But with such intriguing findings in an area of study that's important to millions of people worldwide, you can bet that follow-up research is already in the works.

In the meantime, the good news is that the data say we can benefit from as little as 10 minutes of exercise per day. That's a walk around the block, a couple of laps in the pool or a few flights of stairs at work instead of the elevator.

We hope you'll give it a try and, after a few months, will let us know how you're doing.

Eve Glazier, M.D., MBA, is an internist and assistant professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and primary care physician at UCLA Health.